1. Field of the Invention
This invention relates generally to a rotary-to-linear motion actuator having a helical bevel gear and methods of use thereof, and more particularly to a fluid flow apparatus having a helical bevel gear for controlling the flow of a fluid by means of changing the area of a flow passage.
2. Description of the Related Art.
When a fluid passes through a restricted passage, it gains speed in the area where the cross section is reduced. Since the energy, according to Bernouilli's law, is conserved, the rise in kinetic energy generates a drop in the pressure energy. The later then rises again when the flow passage cross section area rises again, thereby reducing the speed of the fluid.
The use of a purely mechanical apparatus in which a plug seals against a seat is very widely known, and can be used either to close off the flow altogether or adjust the flow of a fluid by movement of the plug away from the seat. Such a valve is not entirely suitable for use in controlling flows of potentially abrasive fluids, for example the liquids emerging from an oil well that may contain sand particles, as the particulate material will cause abrasion of the valve surfaces especially when the valve is almost closed. In addition, the pressure can locally drop by a large amount and reach values that are lower than the vaporization pressure of this liquid when the flow passage is restricted. When this happens, liquid can vaporize causing small gas bubbles to build up. The rise in pressure due to velocity decrease or contact with a surface then leads to an implosion of these bubbles, which is a highly energetic phenomenon in terms of pressure and temperature which can lead to the surrounding solid surface matter being abraded or torn apart. According to the extent of the cavitation phenomenon, the erosion taking place on the downstream surface of the body can be very quick and the destruction of the apparatus can take only a short amount of time. Consequently, when the apparatus is intended to be used in an application characterized by a large pressure difference, it is necessary to provide a valve that is adapted to withstand such a large pressure difference.
It is desirable to provide an actuator that converts rotary motion to linear motion by means of a bevel gear with teeth arranged on a helix of the same pitch as load bearing threads.
It is therefore further desirable to provide a fluid flow apparatus having a helical bevel gear for controlling the flow of a fluid by means of changing the area of the flow passage.
It is still further desirable to provide a fluid flow apparatus having a helical bevel gear that minimizes the disturbance of the fluid passing through the apparatus, thereby reducing the erosive effect on interior surfaces that force the fluid to change direction.
It is yet further desirable to provide a fluid flow apparatus having a helical bevel gear where the pressure drop through the flow passage is suitably distributed within the apparatus, so as to efficiently protect the apparatus against damage due to cavitation.
It is still yet further desirable to provide a fluid flow apparatus having a variable restriction orifice that is affected by rotating a stem in order to actuate a helical bevel gear to linearly move a contoured plug assembly in a direction normal to the plane of the orifice.